I "got retired" last year, so plunged back into thermionics. Have made some shocking discoveries in the recesses of closets, under guest room beds, back of closets, etc. Like going to an estate sale, but the Dearly Departed was me...
One big surprise was an untouched Bogen DB-130 Mono amp, the original Unnecessarily Complex tube amp. Apparently dates from circa 1955.
Uses 6AV5GA power tubes with a 6CG7 voltage regulator and final driver.
Plus the usual chorus line of 12AX7s and a 12AU7 for the phone stage.
WHAT TO DO? I am totally flummoxed by this one.
I DO have a Mono LP dedicated system (currently using a PhonoDude phono preamp and 300B/417A TubeLab power amp), so I COULD actually use this amp in a restored condition.
Some options:
(a) Sell on eBay untouched.
(b) scrounge tubes (think I have them all), bring-up slowly on Variac & hope the power caps reform (ie don't spew), then reappraise. Then, for example:
(c) recap the power supply; just finished doing this on an old battered QUAD 303 closet find, worked great without any other alterations.
(d) rewire an input bypassing the phono stage and tone controls, use as power amp.
(e) re-use the iron and sockets for a screen drive 6AV5GA P-P amp. Haven't studied this option, but I'm guessing it could be done within the confines of the chassis.
(f) Sell on eBay as working amp...
The build quality is spectacular, so it pains me to think about dissecting it, but I'm afraid it's merely an example of 1950's peak tube amp complexity, and doesn't promise to do any one thing very well (which is why they continue to be quite cheap; super clean working DB-230s (6V6s) are going for say $200 now.
PLUS, it is VERY crowded under there. I reckon that a full-on restoration would take a man-month.
PS have a pile of 6AV5GAs. Running them in the shop in a heavily modified TubeLab Simple SE at 23W dissipation.
PPS did just upgrade to a nice LCR, so I could take a sweep of the components to see if there are any clunkers...
All opinions appreciated.
One big surprise was an untouched Bogen DB-130 Mono amp, the original Unnecessarily Complex tube amp. Apparently dates from circa 1955.
Uses 6AV5GA power tubes with a 6CG7 voltage regulator and final driver.
Plus the usual chorus line of 12AX7s and a 12AU7 for the phone stage.
WHAT TO DO? I am totally flummoxed by this one.
I DO have a Mono LP dedicated system (currently using a PhonoDude phono preamp and 300B/417A TubeLab power amp), so I COULD actually use this amp in a restored condition.
Some options:
(a) Sell on eBay untouched.
(b) scrounge tubes (think I have them all), bring-up slowly on Variac & hope the power caps reform (ie don't spew), then reappraise. Then, for example:
(c) recap the power supply; just finished doing this on an old battered QUAD 303 closet find, worked great without any other alterations.
(d) rewire an input bypassing the phono stage and tone controls, use as power amp.
(e) re-use the iron and sockets for a screen drive 6AV5GA P-P amp. Haven't studied this option, but I'm guessing it could be done within the confines of the chassis.
(f) Sell on eBay as working amp...
The build quality is spectacular, so it pains me to think about dissecting it, but I'm afraid it's merely an example of 1950's peak tube amp complexity, and doesn't promise to do any one thing very well (which is why they continue to be quite cheap; super clean working DB-230s (6V6s) are going for say $200 now.
PLUS, it is VERY crowded under there. I reckon that a full-on restoration would take a man-month.
PS have a pile of 6AV5GAs. Running them in the shop in a heavily modified TubeLab Simple SE at 23W dissipation.
PPS did just upgrade to a nice LCR, so I could take a sweep of the components to see if there are any clunkers...
All opinions appreciated.
Attachments
One more thing; looking at the front panel, I seem to remember that I bought this (cheap) with the idea that it could be restored and used to "transcribe" old vinyl (and shellac, for that matter) to digital.
Note the equalization options available. Don't see that stuff anymore.
A lot of motivation for that application has disappeared with digital resissues and high-end streaming services...
Note the equalization options available. Don't see that stuff anymore.
A lot of motivation for that application has disappeared with digital resissues and high-end streaming services...
I look at all those amplifier features that increase the complexity, and which requires more work to restore caps, switches, potentiometers, tubes, etc.
Back then, Marketing sales brochures had check mark boxes of features to put side by side with their competitors. Or if not a side by side, just a very large listing of features on the brochure.
Most people never used 1/2 of those features, but they were persuaded to purchase on the basis that they might need that feature someday.
All that reminds me of my multiple generations of digital cameras.
(I started with film photography. 35mm, then medium format, then 4x5 large format,
then selling all the 4x5 gear).
The multiple generations of digital cameras had more and more features, about 1/2 of which almost nobody ever uses.
Marketing is at work again.
One thing that multiple features of amplifiers, and multiple features of digital cameras have in common, is that the average customer has one or more feature adjusted completely wrong for the customer's application. But that is only an optimistic viewpoint.
I did Electronic Test and Measurement product Marketing for 5 years.
I guess I am just jaded.
Back then, Marketing sales brochures had check mark boxes of features to put side by side with their competitors. Or if not a side by side, just a very large listing of features on the brochure.
Most people never used 1/2 of those features, but they were persuaded to purchase on the basis that they might need that feature someday.
All that reminds me of my multiple generations of digital cameras.
(I started with film photography. 35mm, then medium format, then 4x5 large format,
then selling all the 4x5 gear).
The multiple generations of digital cameras had more and more features, about 1/2 of which almost nobody ever uses.
Marketing is at work again.
One thing that multiple features of amplifiers, and multiple features of digital cameras have in common, is that the average customer has one or more feature adjusted completely wrong for the customer's application. But that is only an optimistic viewpoint.
I did Electronic Test and Measurement product Marketing for 5 years.
I guess I am just jaded.
You surely own a piece of hifi history, of the golden age of analog tube audio.
If you want to use it, try it out. If it hums, do something on the PSU network, but don't do a total renew restoration that doesn't leave anything original inside. Because it destroys an original. Or just leave it on the shelf just for showing an original, untouched and rare item.
There are not so many out there, and every day they get more rare.
Btw, most people know the price of anything, but not the value.
Value it does have, because it have its own, unique sound and being build from the best parts in audio history. Not build by crappy asian parts like today.
The value of many things is much higher to the owner than the price tag reflects.
Bogen is just one of those unfamed companies where people think that they just have produced this school auditorium tube gear. Well, that may be...its the best to let them think this way.
Bogen made some serious tube amps.
The history of those electric parts is more than 100 years long, and this unit use the best (or nearly the best, because its consumer gear) of parts at the height of the famous american tube sound.
It was the era of Saturn V rockets and other famous US gear, that has been never surpassed in quality- even until today. The time, when in the US and with US parts companies have build gear, that could last a lifetime and still sounds great.
Remember, that will not happen again. Compare the sound of a new, asian tube gear with this one and you will hear it instantly. Many companies build great gear those times, all long gone and when still in business, its just ******** quality and sound they produce today. Ask Saul Marantz, what he thinks of todays companies products. Its just crap, but with a nice looking front plate. You own the real thing, don't let it go on ebay for a cheap buck. You will not get this again, for sure.
If you want to use it, try it out. If it hums, do something on the PSU network, but don't do a total renew restoration that doesn't leave anything original inside. Because it destroys an original. Or just leave it on the shelf just for showing an original, untouched and rare item.
There are not so many out there, and every day they get more rare.
Btw, most people know the price of anything, but not the value.
Value it does have, because it have its own, unique sound and being build from the best parts in audio history. Not build by crappy asian parts like today.
The value of many things is much higher to the owner than the price tag reflects.
Bogen is just one of those unfamed companies where people think that they just have produced this school auditorium tube gear. Well, that may be...its the best to let them think this way.
Bogen made some serious tube amps.
The history of those electric parts is more than 100 years long, and this unit use the best (or nearly the best, because its consumer gear) of parts at the height of the famous american tube sound.
It was the era of Saturn V rockets and other famous US gear, that has been never surpassed in quality- even until today. The time, when in the US and with US parts companies have build gear, that could last a lifetime and still sounds great.
Remember, that will not happen again. Compare the sound of a new, asian tube gear with this one and you will hear it instantly. Many companies build great gear those times, all long gone and when still in business, its just ******** quality and sound they produce today. Ask Saul Marantz, what he thinks of todays companies products. Its just crap, but with a nice looking front plate. You own the real thing, don't let it go on ebay for a cheap buck. You will not get this again, for sure.
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Opinions vary. Mine is that these fine "vintage" pieces exist solely to make sound, not looking pretty on a shelf.
Either you sell it or you restore the piece to full functionality, while remaining faithful to the original design concepts. Modern parts may allow for a level of performance, within the designer's concepts, that that person could only fantasize about. Today's vastly improved electrolytic caps. are a case in point.
Either you sell it or you restore the piece to full functionality, while remaining faithful to the original design concepts. Modern parts may allow for a level of performance, within the designer's concepts, that that person could only fantasize about. Today's vastly improved electrolytic caps. are a case in point.
Modern parts have not the sound signature of old parts.
Maybe they measure better, but don't sound better.
Replace all old with modern parts and you'll get a different sounding amp.
You may like it or not, but for a real collector an oldtimer Mercedes with parts of a new car is worth nothing. Not many collectors of amps have understood this fact, but like to swap all old for new parts.
An original restoration restores damaged parts with NOS parts that are working. Not old with super modern parts.
Maybe they measure better, but don't sound better.
Replace all old with modern parts and you'll get a different sounding amp.
You may like it or not, but for a real collector an oldtimer Mercedes with parts of a new car is worth nothing. Not many collectors of amps have understood this fact, but like to swap all old for new parts.
An original restoration restores damaged parts with NOS parts that are working. Not old with super modern parts.
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With all respect, we don't know what new parts from the time the unit was originally constructed sound like. We do know that aging has had a considerable adverse effect.
Agreed and understood.
My notion of “restoration” is replacing out-of spec parts with modern equivalents.
For example, all of the tall power supply and output electrolytic caps on my beat-up Quad 303 power amp were completely shot (showing picofarad values instead of the nominal 2000uF. Replaced those with 4700uf caps (“utility” Nichicons on P/S and “audiophile” on the output. Fit in the same space, only half the height.
Only change was flipping the caps to terminal end up- but QUAD did the same thing on the later serial numbers...
On the Bogen I would definitely replace the power supply caps, and MEASURE all the smaller caps and resistors to replace only the ones out of spec...
My notion of “restoration” is replacing out-of spec parts with modern equivalents.
For example, all of the tall power supply and output electrolytic caps on my beat-up Quad 303 power amp were completely shot (showing picofarad values instead of the nominal 2000uF. Replaced those with 4700uf caps (“utility” Nichicons on P/S and “audiophile” on the output. Fit in the same space, only half the height.
Only change was flipping the caps to terminal end up- but QUAD did the same thing on the later serial numbers...
On the Bogen I would definitely replace the power supply caps, and MEASURE all the smaller caps and resistors to replace only the ones out of spec...
If it were me, I'd flip it. Take the $200 - if you can get it, looks nice - and run.
The problem as I see it is the one suggested above - new components will make it sound different. Consider the difficulty of getting NOS vintage parts, just for starters. Period correct NOS coupling caps that dont leak voltage. On top of everything else it's going to need...
Now, if you played electric guitar, I might be suggesting something different ;') There, the inspiration would be building your own sound as you restore a more minimal circuit (w/o so many input signal connectors, switching needing to be restored) to reliable operating condition.
The problem as I see it is the one suggested above - new components will make it sound different. Consider the difficulty of getting NOS vintage parts, just for starters. Period correct NOS coupling caps that dont leak voltage. On top of everything else it's going to need...
Now, if you played electric guitar, I might be suggesting something different ;') There, the inspiration would be building your own sound as you restore a more minimal circuit (w/o so many input signal connectors, switching needing to be restored) to reliable operating condition.
All the 'lytics have long since dried out. Waxed paper signal caps. may or may not have started to leak. Soviet surplus K40 paper in oil (PIO) parts could be a reasonable replacement there.
Looks like a lot of work to restore. I would put that on eBay. My guess is it goes to South Korea or Japan.
In my late teens I made a guitar amp out of a Bogen Challenger PA. I think it was a 30 watt version, but I'm not sure, I didn't have it too long before it was stolen out of my car. A bunch of us were making a racket with it at a recording studio where I spent much of my free time. Several local musicians played through it and many liked it's character. Too many people knew I worked at the Olson Electronics store, where it vanished while I was at work.
I also made a couple of guitar amps out of Stromberg Carlson PA amps that ran 4 X 6L6GA's. I liked them better than the Bogen, but wound up selling them 50+ years ago. A couple years ago I ran across a similar Stromberg at a hamfest, so I bought it......yet another project.
Some very excellent points.
Certainly the first thing is to scrounge some tubes and VARIAC-up, like we say in Texas, so see what we got here.
If it makes noise and the smoke doesn’t get released, then take measurements across the expensive/suspect components, starting with the caps, generally highest to lowest values, I guess.
Good suggestion about Russian PIO caps. Have a bunch of those & like the sound/ price ratio, plus they’re “correct-tech”.
HAD NOT THOUGHT of the electric guitar amp angle...I do have all manner of guitars, and amps, and cabs...including some nice ALNICO stuff. Not a real “player” though.
Seems like it would be easier to get a nice saggy, clippy guitar amp by starting from scratch rather than extracting the “high fidelity” out of this one...just a thought.
IF it needs major surgery (e.g. MANY components out of spec) what about a screen-drive 6AV5GA conversion? TubeLab George?
There’s enough power, more than enough sockets, I have 6AV5s...
Certainly the first thing is to scrounge some tubes and VARIAC-up, like we say in Texas, so see what we got here.
If it makes noise and the smoke doesn’t get released, then take measurements across the expensive/suspect components, starting with the caps, generally highest to lowest values, I guess.
Good suggestion about Russian PIO caps. Have a bunch of those & like the sound/ price ratio, plus they’re “correct-tech”.
HAD NOT THOUGHT of the electric guitar amp angle...I do have all manner of guitars, and amps, and cabs...including some nice ALNICO stuff. Not a real “player” though.
Seems like it would be easier to get a nice saggy, clippy guitar amp by starting from scratch rather than extracting the “high fidelity” out of this one...just a thought.
IF it needs major surgery (e.g. MANY components out of spec) what about a screen-drive 6AV5GA conversion? TubeLab George?
There’s enough power, more than enough sockets, I have 6AV5s...
GAAAK I checked inventory, and have only ONE 6CG7/6FQ7.
Quick order on ebay for some "tests as new" tubes, but it'll be a couple of days.
BTW did NOT know 6CG7 was a 6SN7 9-pin equivalent, so that's good to know.
Is there another equivalent that I am missing, and might be in inventory?
Couldn't find one...
Quick order on ebay for some "tests as new" tubes, but it'll be a couple of days.
BTW did NOT know 6CG7 was a 6SN7 9-pin equivalent, so that's good to know.
Is there another equivalent that I am missing, and might be in inventory?
Couldn't find one...
6FQ7 is a 100% compatible substitute for the 6CG7. Many times, a 6GU7 (basically a "6" V. version of the 12BH7) substitutes successfully for the 6CG7.
Yeah, nah, don’t have either 6FQ7 or 6GU7. It’ll just be a few days for the real things to arrrive. In the meantime, I guess could stick some rectifiers in there and warm-up those PS caps with the VARIAC, IF I have a minute. I could get as far as looking at the raw B+...
However, one of the 6CG7s is used as a voltage regulator tube (1/2 pass tube, 1/2 error amp I guess) so I’m dead in the water until I get those...
However, one of the 6CG7s is used as a voltage regulator tube (1/2 pass tube, 1/2 error amp I guess) so I’m dead in the water until I get those...
Quick question in schematic interpretation, since I don’t have a manual for this puppy:
Is diode H373 (adjacent to the 5Y3 rectifier tubes) a 55 volt Zener?
It’s in the right place for a Voltage reference, and has -55V marked above it. If it walks like a duck, and regulates like a duck...
It isn’t marked with the modern Z squiggle, but this schematic may predate that convention.
Can’t find an H373 zener anywhere, but that might just be a Bogen part number, or so obsolete it has disappeared from view...
Is diode H373 (adjacent to the 5Y3 rectifier tubes) a 55 volt Zener?
It’s in the right place for a Voltage reference, and has -55V marked above it. If it walks like a duck, and regulates like a duck...
It isn’t marked with the modern Z squiggle, but this schematic may predate that convention.
Can’t find an H373 zener anywhere, but that might just be a Bogen part number, or so obsolete it has disappeared from view...
Oh, crap, never mind. It’s just a normal diode taken off a 55 volt TAP on the transformer.
Hard-wired, half-rectified voltage reference, with the advantage that it’s proportional to the secondaries...
I got excited to see a Zener from 1955 that I forgot that there wasn’t such a thing.
Tragically, that means I am older than Zener diodes.
Hard-wired, half-rectified voltage reference, with the advantage that it’s proportional to the secondaries...
I got excited to see a Zener from 1955 that I forgot that there wasn’t such a thing.
Tragically, that means I am older than Zener diodes.
1955 you say. IIRC, Sarkes Tarzian introduced the M500 silicon diode later than that. As a youngster, I learned the hard way about peak surge limiting by wrecking 1 of those. 
Perhaps H373 is a selenium rectifier of some sort.
Perhaps H373 is a selenium rectifier of some sort.
